[clang] [Clang][HTO] Add clang attribute for propagating llvm-level information (PR #83059)

[William Moses via cfe-commits]

https://github.com/wsmoses updated https://github.com/llvm/llvm-project/pull/83059

>From b6ab7f38406cd51670bd2a1253142243cf80a433 Mon Sep 17 00:00:00 2001
From: "William S. Moses" <gh at wsmoses.com>
Date: Mon, 26 Feb 2024 16:17:55 -0500
Subject: [PATCH] [Clang][HTO] Add clang attribute for propagating llvm-level
 information

---
 clang/include/clang/Basic/Attr.td     |  7 +++++++
 clang/include/clang/Basic/AttrDocs.td | 13 +++++++++++++
 clang/lib/CodeGen/CGCall.cpp          |  9 +++++++++
 clang/lib/CodeGen/CodeGenFunction.cpp | 11 +++++++++++
 clang/test/CodeGen/attr-llvmfn.c      | 14 ++++++++++++++
 5 files changed, 54 insertions(+)
 create mode 100644 clang/test/CodeGen/attr-llvmfn.c

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index fa191c7378dba4..044f4fada3590f 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -2211,6 +2211,13 @@ def AllocAlign : InheritableAttr {
   let Documentation = [AllocAlignDocs];
 }
 
+def LLVMFuncAttr : InheritableAttr {
+  let Spellings = [Clang<"llvm_fn_attr">];
+  let Args = [StringArgument<"LLVMAttrName">, StringArgument<"LLVMAttrValue">];
+  let Documentation = [LLVMFuncAttrDocs];
+  let InheritEvenIfAlreadyPresent = 1;
+}
+
 def NoReturn : InheritableAttr {
   let Spellings = [GCC<"noreturn">, Declspec<"noreturn">];
   // FIXME: Does GCC allow this on the function instead?
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index b96fbddd51154c..3f93bb6d6fc648 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -781,6 +781,19 @@ pointer is not sufficiently aligned.
   }];
 }
 
+def LLVMFuncAttrDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Use ``__attribute__((llvm_fn_attr(attr_name, attr_value)))`` on a function to specify an LLVM function attribute that will be added to this function. 
+
+Note that uses of this attribute are highly compiler specific as the meaning and availability of LLVM attributes may change between compiler versions.
+
+This attribute is only intended for advanced users who need to specify specific information only available in LLVM attributes. Use of attributes which are not tied to a specific version of Clang (e.g. pure) should be preferred when available.
+
+The first arugment is a string representing the name of the LLVM attribute to be applied and the second arugment is a string representing its value.
+  }];
+}
+
 def EnableIfDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index d05cf1c6e1814e..0d6e1cb5124037 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2465,6 +2465,15 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
 
     if (TargetDecl->hasAttr<ArmLocallyStreamingAttr>())
       FuncAttrs.addAttribute("aarch64_pstate_sm_body");
+
+    for (auto Attr : TargetDecl->specific_attrs<LLVMFuncAttr>()) {
+      auto name = Attr->getLLVMAttrName();
+      auto value = Attr->getLLVMAttrValue();
+
+      auto Attr = llvm::Attribute::parseAttr(
+          getLLVMContext(), AttributeAndValue.first, AttributeAndValue.second);
+      FuncAttrs.addAttribute(Attr);
+    }
   }
 
   // Attach "no-builtins" attributes to:
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 1ad905078d349c..86ada81facb5e3 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -831,6 +831,17 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
         FD->getBody()->getStmtClass() == Stmt::CoroutineBodyStmtClass)
       SanOpts.Mask &= ~SanitizerKind::Null;
 
+  if (D) {
+    for (auto Attr : TargetDecl->specific_attrs<LLVMFuncAttr>()) {
+      auto name = Attr->getLLVMAttrName();
+      auto value = Attr->getLLVMAttrValue();
+
+      auto Attr = llvm::Attribute::parseAttr(
+          getLLVMContext(), AttributeAndValue.first, AttributeAndValue.second);
+      Fn->addFnAttr(Attr);
+    }
+  }
+
   // Apply xray attributes to the function (as a string, for now)
   bool AlwaysXRayAttr = false;
   if (const auto *XRayAttr = D ? D->getAttr<XRayInstrumentAttr>() : nullptr) {
diff --git a/clang/test/CodeGen/attr-llvmfn.c b/clang/test/CodeGen/attr-llvmfn.c
new file mode 100644
index 00000000000000..72f14a726f795e
--- /dev/null
+++ b/clang/test/CodeGen/attr-llvmfn.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -debug-info-kind=limited -emit-llvm -o - | FileCheck %s
+
+void t1() __attribute__((llvm_fn_attr("custom_attr", "custom_value"), llvm_fn_attr("second_attr", "second_value")));
+
+void t1()
+{
+}
+
+void t2();
+
+void t3() {
+	t2() ____attribute__((llvm_fn_attr("custom_attr", "custom_value"), llvm_fn_attr("second_attr", "second_value")));
+}
+